Method of manufacturing pneumatic tire

ABSTRACT

A method of manufacturing a pneumatic tire comprises assembling unvulcanized rubber components to make a green tire, vulcanizing the green tire, and winding an unvulcanized rubber tape so that the windings collectively have a predetermined cross sectional shape for at least one of the unvulcanized rubber components to thereby make said at least one of the unvulcanized rubber components.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a pneumatictire whose rubber components are formed by winding a unvulcanized rubbertape.

2. Description of the Related Art

Conventionally, unvulcanized rubber tires are made of unvulcanizedrubber components having various shapes and sizes. As the unvulcanizedrubber components are formed by extruders, the number and sizes of theextruders are depend on the maximum size and the number of the kinds ofthe rubber components. Usually, at least several extruders which arerelatively large-sized are required.

In recent years, in order to decrease the number and size of extrudersto decrease the plant size and to establish a flexible manufacturingsystem, it was proposed to make a pneumatic tire by winding anunvulcanized rubber tape around a drum directly or indirectly thereoninstead of applying a rubber component. In this method, as shown inFIG.11, an unvulcanized rubber tape T is wound into a target crosssectional shape similar to the final shape of the rubber component bycontrolling the overlaps of the windings of the tape.

Therefore, it became possible to make rubber components having variousshapes and sizes.

In general, different rubber components of a tire are usually made ofdifferent rubber compounds. If the method of making a rubber componentis simply changed from the extruding into a final shape to the windinginto a final shape, it is still necessary to prepare variousunvulcanized rubber tapes made of different rubber compounds.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a method ofmanufacturing a pneumatic tire, by which it is possible to establish aflexible manufacturing system and to decrease the plant size, whereasanother object of the present invention is to increase the number ofrubber components which are made by winding an unvulcanized rubber tape.Still another object of the present invention is to decrease the numberof unvulcanized rubber tapes used in a tire.

According to the present invention, a method of manufacturing apneumatic tire comprises assembling unvulcanized rubber components tomake a green tire, vulcanizing the green tire, and winding anunvulcanized rubber tape so that the windings collectively have apredetermined cross sectional shape for at least one of the unvulcanizedrubber components to thereby make said at least one of the unvulcanizedrubber components.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in detail inconjunction with the accompanying drawings.

FIGS. 1 a, 1 b and 1 c show unvulcanized rubber tapes for making rubbercomponents.

FIG. 2 is a cross sectional view of a pneumatic tire.

FIGS. 3 a–3 g are diagrams for explaining a method of manufacturing apneumatic tire according to the present invention.

FIGS. 4 a–4 c are diagrams for explaining a modification of the method.

FIG. 5 is a diagram for explaining an apparatus for making and winding arubber tape.

FIG. 6 shows a rubber component formed by winding an unvulcanized rubbertape including short fibers having a variable degree of orientation.

FIGS. 7 a and 7 b each show a sidewall rubber.

FIG. 8 is a cross sectional view of a pneumatic tire.

FIG. 9 is a partial sectional view of a sidewall portion.

FIG. 10 is a partial sectional view of a sidewall portion.

FIG. 11 is a sectional view of a unvulcanized rubber component formed bywinding an unvulcanized rubber tape.

DETAILED DESCRIPTION

According to the present invention, tire components are formed bywinding a long unvulcanized rubber tape T. The unvulcanized rubber tapeT means a pure rubber tape Tp made of unvulcanized rubber only, a fibercontaining rubber tape Trf made of unvulcanized rubber with short fibersmixed therein, and a cord containing rubber tape Trc made ofunvulcanized rubber in which one or more cords are embedded along thelength of the tape. FIGS. 1 a, 1 b and 1 c show examples of the purerubber tape Tp, fiber containing rubber tape Trf and cord containingrubber tape Trc, respectively. The thickness (T) of the unvulcanizedrubber tape T may be set in a range of from 0.3 to 2.5 mm, preferably ina range of from 0.5 to 2.0 mm. The width W of the unvulcanized rubbertape T may be set in a range of from 5 to 50 mm preferably in a range offrom 10 to 25 mm.

The present invention can be applied to various pneumatic tires, e.g.passenger car tires, light truck tires, motorcycle tires, heavy dutytires and the like. However, for the sake of convenience, the followingdescriptions are made based on passenger car radial tires having a lowaspect ratio.

In the drawings, pneumatic tire 1 comprises a tread portion 2, a pair ofsidewall portions 3, a pair of bead portions 4 each with a bead core 5therein, a carcass 6 extending between the bead portions 4, and a treadreinforcing belt disposed radially outside the carcass 6 in the treadportion 2.

The carcass 6 comprises at least one ply 6A of cords arranged radiallyat an angle of from 75 to 90 degrees with respect to the tire equator C,extending between the bead portions 4 through the tread portion 2 andsidewall portions 3, and turned up around the bead core 5 in each beadportion 4 from the inside to the outside of the tire so as to form apair of turnups 6 b and the main 6 a therebetween. For the carcasscords, organic fiber cords, e.g. polyester, nylon, rayon, aramid and thelike or steel cords are used. The exemplary carcass 6 shown in thedrawings is composed of a single ply 6A of organic fiber cords arrangedradially at 90 degrees, and the carcass ply turnups 6 b extend radiallyoutwardly beyond the maximum section width point of the carcass main 6b.

The tread reinforcing belt comprises a breaker 7 and a optional banddisposed on the radially outside of the breaker 7.

The breaker 7 is disposed on the crown portion of the carcass 6 andcomprises at least two cross plies 7A and 7B of cords laid parallel witheach other at an angle of from 10 to 45 degrees with respect to the tireequator. For the breaker cords, steel cords and high-modulus organiccords such as aramid fiber cords can be used.

The band is disposed on the radially outside of the breaker 7 and madeof cord(s) laid at almost zero angle or a small angle with respect tothe circumferential direction of the tire. Preferably, the band isformed by spirally winding at least one organic fiber cord, e.g. nylonand the like, at an angle of not more than 5 degrees with respect to thetire equator. In case that a plurality of band cords are spirally wound,a rubber tape Trc in which band cords are embedded along the lengththereof as shown in FIG. 1 c, is preferably used.

The exemplary belt shown in the drawings is composed of a breaker 7 madeup of two cross plies of steel cords.

A pneumatic tire is compose of various rubber components. In the treadportion 2, a tread rubber Gt is disposed radially outside the belt. Ineach of the sidewall portions 3, a sidewall rubber Gs is disposedaxially outside the carcass 6 defining a part of the outer surface ofthe tire. In each of the bead portions 4, a clinch rubber Gbc isdisposed along the axially outer surface and bottom surface of the beadportion, and a bead apex rubber Gba is further disposed on the radiallyoutside of the bead core 5 and extends radially outwardly therefromwhile tapering towards its radially outer end. On the inside of thecarcass 6, an inner liner rubber Gil made of an air-impermeable rubbercompound may disposed to cover the inner surface of the tireair-tightly. In the exemplary tires shown in the drawings, the bead apexrubber Gba is made of a hard rubber compound and disposed between thecarcass main 6 a and turnup 6 b and terminates on the radially inside ofthe radially outer end of the turnup 6 b.

In the following examples tires, at least the sidewall rubber Gs isformed by winding a long unvulcanized rubber tape T.

FIG. 2 shows a radial tire for passenger cars in its normally inflatedunloaded state.

Here, the normally inflated unloaded state is such that the tire ismounted on a standard wheel rim and inflated to a standard innerpressure but loaded with no tire load. The standard rim is the “standardrim” specified in JATMA, the “Measuring Rim” in ETRTO, the “Design Rim”in TRA or the like. The standard pressure is the “maximum air pressure”in JATMA, the “Inflation Pressure” in ETRTO, the maximum pressure givenin the “Tire Load Limits at Various Cold Inflation Pressures” table inTRA or the like. In case of passenger car tires, however, 180 kPa isused as the standard pressure. Incidentally, the standard load is the“maximum load capacity” in JATMA, the “Load Capacity” in ETRTO, themaximum value given in the above-mentioned table in TRA or the like.

In this example, in addition to the above-mentioned rubber components, athin under tread rubber Gut is disposed between the belt 7 and the treadrubber Gt to improve the adhesion between the belt 7 and the treadrubber Gt.

Further, a cushion rubber Gtc is disposed between the axially outeredges 7 e of the belt 7 and the carcass 6 in order to mitigate stress onthe belt edge. Preferably, the axial overlap width CW of the cushionrubber Gtc and the belt 7 is set in a range of from 0.05 to 0.25 timespreferably 0.07 to 0.2 times the axial width BW of the belt 7. Thecushion rubber Gtc tapers from its middle point towards each sidethereof.

Furthermore, each of the sidewall portiens portions 3 is providedbetween the carcass 6 and the inner liner rubber Gil with an insulationrubber Gin to prevent a separation of the inner liner rubber Gil fromthe carcass 6. The insulation rubber Gin extends at least between aposition near the axially outer end of the belt 7 and a positionradially inwards of the maximum section width point of the carcass main6 a. Preferably, the insulation rubber Gin overlaps with the belt 7 byan axial width LW in a range of from 0.2 to 0.5 times preferably 0.2 to0.4 times the axial width BW of the belt 7. On the other hand, theradially inner end of the insulation rubber Gin is spaced radiallyinwardly from the maximum section width point of the carcass main by aradial distance Ha in a range of not less than 0.1 times preferably 0.3to 0.4 times the tire section height. In this example, the radiallyinner end of the insulation rubber Gin is positioned radially inside theradially outer end of the bead apex rubber Gba.

The above-mentioned clinch rubber Gbc comprises a base part extendingalong the bottom face of the bead portion 4, and an axially outer partand an axially inner part extending along the axially outer surface andaxially inner surface of the bead portion 4, respectively.

The above-mentioned sidewall rubber Gs is spliced with the tread rubberGt and the axially outer part of the clinch rubber Gbc.

It is desirable for decreasing the number of different kinds ofunvulcanized rubber tapes T, that a plurality of rubber componentsshould be formed by winding an unvulcanized rubber tape T. This meansthat these rubber components are made of an identical rubber compound.It is however, not always necessary that the rubber tape T has aconstant thickness and a constant width because the thickness and/orwidth can be changed during winding by means of rolling and the like.Further, it is not always necessary that the rubber tape T is continuousbetween the rubber components. The rubber tape T may be cut if need be.The important thing is to use a rubber tape formed by one apparatuswhich may include an extruder and rollers.

In this embodiment, the sidewall rubber Gs, insulation rubber Gin andcushion rubber Gtc are formed by winding a pure rubber tape Tp1, namely,these are made of the identical rubber compound.

The clinch rubber Gbc is formed by winding a pure rubber tape Tp2 madeof a different rubber compound.

The inner liner rubber Gil is formed by winding a pure rubber tape Tp3made of a different air-impermeable rubber compound.

As the inner liner rubber Gil is used to provide the tire inner surfacewith air-tightness, a butyl-base rubber compound is used for theunvulcanized rubber tape Tp3, which includes at least 50 parts by weightof butyl rubber or a derivative thereof with respect to 100 parts byweight of the base rubber. For the deliberative of butyl rubber,halogenated butyl rubber such as chlorinated butyl rubber, brominatedbutyl rubber and the like is used.

As the sidewall rubber Gs, cushion rubber Gtc and insulation rubber Ginare disposed in regions where deformation is relatively large, therubber components are subjected to mechanical fatigue. Accordingly, itis very important to prevent separation failure between the windings ofthe rubber tape Tp1 and cracks on the tire outer surface along theboundaries therebetween. The sidewall rubber Gs should be superior inthe cut resistance, weatherproof, flexibility and the like.

On the other hand, the clinch rubber Gbc is pressed and rubs against thewheel rim and it is necessary to provide the bead portion with rigidity.

Therefore, a rubber compound which is relatively hard and superior inthe resistance to abrasion is used for the unvulcanized rubber tape Tp2forming the clinch rubber Gbc.

For the unvulcanized rubber tape Tp1, however, a non-butyl-based rubbercompound superior in adhesion and elasticity is used, which includes 40to 100 parts by weight of a low viscosity polybutadiene rubber and atleast 2.5, preferably at least 2.7, more preferably 3.0 to 4.0 parts byweight of age resistor with respect to 100 parts by weight of the rubbercomponent thereof. The Mooney viscosity of the low viscositypolybutadiene rubber is set in a range of not more than 40, preferablyfrom 28 to 38, more preferably 25. to 35 {ML(1+4) @100 deg. C.}.

For the age resistor, for example,

-   N-phenyl-N′-isopropyl-p-phenylenediamine,-   N-(1,3-dimethylbutyl)-N′phenyl-p-phenylenediamine,-   diallyl-p-phenylenediamine mixture,-   N,N′-diphenyl-p-phenylenediamine,-   p-(p-toluenesulphenylamino)diphenylamine,-   octylatediphenylamine,-   polymer of 2,2,4-trimethyl-1,2-dihydroquinoline,-   6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline,-   N-phenyl-1-naphthylamine,-   4,4′-(alpha,alpha-dimethylbenzyl)dithiocarbamate,-   N,N′-di-2-naphthyl-p-phenylenediamine,-   nickel-dimethyldithiocarbamate,-   nickel-dibutyldithiocarbamate,-   2-mercaptobenzimidazole,-   zinc salt of 2-mercaptobenzimidazole,-   2-mercaptomethylbenzimidazole,-   zinc salt of 2-mercaptomethylbenzimidazole,-   1,3-bis(dimethylaminopropyl)-2-tiourea,-   tributyltiourea,-   N-phenyl-N′-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine    and the like may be used.

The sidewall rubber Gs, cushion rubber Gtc and insulation rubber Gin,namely, the rubber tape Tp1 when vulcanized have a 100% modulus of from0.5 to 2.5 MPa preferably 0.5 to 2.0 MPa more preferably 0.7 to 2.0 MPa,and a JIS type-A-durometer hardness of not more than 65 degreespreferably 40 to 65 degrees more preferably 50 to 62 degrees.

If the 100% modulus is less than 0.5 MPa, the rigidity becomesinsufficient for the sidewall portion 3 and it is difficult to maintainthe steering stability. If the 100% modulus is more than 2.5 MPa and/orthe JIS type-A-durometer hardness is more than 65 degrees, then it isdifficult for the cushion rubber Gtc to mitigate the stress on the beltedge, and it is difficult to provide necessary elasticity for thesidewall rubber Gs.

The following table shows an example of the rubber compound of therubber tape Tp1.

(parts by weight) Natural rubber 40 Low viscosity polybutadiene rubber60 FEF 50 Aromatic oil 5 Age resistor 3 Wax 1.5 Stearic acid 2.5 Zincoxide 3.0 Vulcanization accelerator 1.0 Sulfur 1.5 JIS type-A-durometerhardness  55 *3 100% modulus 1.1 *3 MPa *1 Mooney viscosity: 30{ML(1 +4) @ 100 deg. C.} *2 N-(1,3-dimethylbutyl)-N′phenyl-p-phenylenediamine*3 vulcanizing conditions: 160 deg. C., 18 minutes

The above-mentioned JIS type-A-durometer hardness is measured accordingto the Japanese Industrial Standard K6253. The Mooney viscosity ismeasured according to the Japanese Industrial Standard K6300.

The above-mentioned pneumatic tire 1 can be made as shown in FIGS. 3 ato 3 g.

First, as shown in FIG. 3 a, the above-mentioned tape Tp2 is wound on acylindrical tire building drum D to make the clinch rubber Gbc on eachside of the drum center while leaving a space therebetween.

Further, in order to make the inner liner rubber Gil, as shown in FIG. 3b, the tape Tp3 is wound on the cylindrical tire building drum D acrossthe space between the windings of the tape Tp2. The inner liner rubberGil is somewhat overlapped with the clinch rubber Gbc.

Next, as shown in FIG. 3 c, in order to make the insulation rubber Gin,the tape Tp1 is wound on the inner liner rubber Gil.

Then, as shown in FIG. 3 d, in order to make the carcass ply 6A, a wideraw strip of rubberized carcass cords is applied thereon. Further, thebead core 5 and raw bead apex rubber Gba are placed in each of thecorresponding positions on the wound carcass strip.

Further, as shown in FIG. 3 e, the edges of the carcass strip 6A arefolded around the respective bead cores 5 together with the greater partof the clinch rubber Gbc.

In order to make the cushion rubber Gtc in the corresponding positionsto the belt edges, the rubber tape Tp1 is wound on the carcass stripinto a substantially triangular sectional shape. Thus the rubber tapeTp1 is used again.

The above-mentioned raw carcass strip 6A and the rubber components wounddirectly or indirectly on the cylindrical drum D are changed into atoroidal shape as shown in FIG. 3 f, while decreasing the distancebetween the bead cores 5. And on the crown portion of the toroidalshaped carcass, an assembly of the tread rubber Gt and belt 7 is set.

Further, as shown in FIG. 3 g, in order to make the sidew all rubber Gsin each of the sidewall portions, the rubber tape Tp1 is wound on theaxially outer face of the carcass 6. The rubber tape Tp1 is used oneagain.

Thus, a green tire is made. The green tire is put in a mold andvulcanized.

The above-mentioned tread rubber and belt assembly may be made asfollows. A raw strip of rubberized breaker cords is applied to or woundon a profiled belt drum to make the breaker 7. In case the belt includesa band, a rubber tape Trc in which one or more band cords are embeddedalong the length thereof is spirally wound. Then, an unvulcanized rubbertape T is wound on the belt to make the under tread rubber Gtu (notshown), and another unvulcanized rubber tape T is wound thereon to makethe tread rubber Gt.

For the unvulcanized rubber tape T of the under tread rubber Gut, anatural-rubber-base rubber compound superior in adhesion is used. Forthe unvulcanized rubber tape T (Tp or Trf) of the tread rubber Gt, arubber compound superior in the wear resistance, heat generation andgrip performance is used.

The sidewall rubber Gs can be made by winding an unvulcanized rubbertape T on the toroidal-shaped carcass as illustrated above. But, asshown in FIGS. 4 a and 4 b, it is also possible to make the sidewallrubber Gs by winding an unvulcanized rubber tape T on the carcass in acylindrical shape, and thereafter the tape T is wound, the carcass,sidewall rubber, etc. are changed into a toroidal shape.

Further, as shown in FIG. 4 c, it is possible to form the sidewallrubber Gs on another drum by winding an unvulcanized rubber tape Ttogether with the clinch rubber Gbc, and then apply the assembly of thesidewall rubber Gs and clinch rubber Gbc to the toroidal shaped carcass.

FIG. 5 schematically shows an apparatus for making and winding anunvulcanized rubber tape T, which comprises an extruder 20 including ascrew and a die, a pair of rollers 21 disposed near the outlet of theextruder's die to adjusting the thickness of the rubber tape T, aplurality of cooling rollers 22, 23 and 24 for cooling the extrudedrubber tape T, a tape applicator 27 which can traverse the building drumD, and rollers for guiding and conveying the rubber tape to theapplicator 27. The material rubber compound fed to the extruder is mixedby the screw and extruded from the die into a flat sectional shape. Theextruded unvulcanized rubber is rolled by the rollers 21. By changingthe gap between the rollers, the thickness of the rubber tape T isadjusted to the target thickness. The rubber tape T is fed to theapplicator 27 through cooling rollers and guide rollers. The rubber tapeT is wound on the building drum D by rotating the building drum D andtraversing the tape applicator 27 to give a predetermined sectionalshape to the windings. The extruding speed, rollers' gap, drum speed,applicator speed, applicator position and the like are controlled by acomputer according to stored programs and outputs of various sensors forthe tape thickness, various positions, various speeds, temperature, etc.If necessary, a tape accumulator may be provided between the extruderand applicator.

In the above-mentioned embodiment, as the specific rubber compound isused in the rubber tape Tp1, the sidewall rubber Gs, insulation rubberGin and cushion rubber Gtc can be made by winding the same rubber tapeTp1 and the resultant tire can display its performance equal to a tiremade by the conventional method.

It may be possible to improve a specific performance of the tire byusing plural kinds of rubber compounds. However, it goes against anobject of the present invention. A solution therefor is to use a fibercontaining rubber tape Trf of which short fibers have a variable degreeof orientation.

The fiber containing rubber tape Trf is made by extruding the fibermixed rubber compound and rolling the extruded compound. The shortfibers in the rubber tape Trf are oriented in the extruding direction orthe longitudinal direction of the tape through these process. It ispossible to control the degree of orientation by changing the thicknessof the rubber tape Trf. The thinner rubber tape has a higher degree oforientation. Thus, the fiber containing rubber tape Trf having avariable degree of orientation includes a thin tape and a thick tape.The thin tape and thick tape may be discontinuous. But, in this example,these are continuous.

Preferably, non-metallic fibers are used for the short fibers F. Forexample, organic fibers, e.g. nylon, polyester, aramid, rayon, vinylon,cotton, cellulosic resin, crystalline polybutadiene and the like andinorganic fibers, e.g. glass fiber, carbon fiber, boron fiber and thelike may be used alone or in combination as far as a sufficient adhesionto the rubber can be obtained. The average length of the short fibers Fis set in a range of from 0.2 to 5 preferably 1.0 to 4.0 millimeters,and the average diameter thereof is in a range of from 10 to 100preferably 50 to 80 micrometers. For example, nylon 66 fibers having anaverage length of 3.5 mm and an average diameter of 70 to 80 micrometersare used.

The content of the short fibers F is set in a range of from 10 to 30preferably 15 to 25 parts by weight with respect to 100 parts by weightof the rubber component of the compound.

For the rubber component, there is used diene rubber such as naturalrubber, isoprene rubber, styrene butadiene rubber, butadiene rubber,chloroprene rubber, acrylonitrile butadiene rubber and the like, aloneor in combination.

Usually, the thickness (t) of the fiber containing rubber tape Trf isset in a range of from 0.3 to 2.5 mm preferably 0.5 to 2.0 mm asmentioned above. And the ratio (t1/t2) of the thickness t1 of the thintape to the thickness t2 of the thick tape is set in a range of from0.15 to 0.80 preferably 0.20 to 0.75 more preferably 0.20 to 0.70. Thewidth W of the rubber tape Trf may be set in a range of from 5 to 50 mmpreferably 10 to 25 mm.

For example, in a rubber component shown in FIG. 6, part A1 is formed bywinding a thin tape Trf1 and part A2 is formed by winding a thick tapeTrf2. As a result, the part A1 may have a higher rigidity than the partA2.

In FIGS. 7 a and 7 b, the sidewall rubber Gs is formed by winding thefiber containing unvulcanized rubber tape Trf. As the short fibers F inthe rubber tape Trf are oriented almost parallel with the longitudinaldirection of the tape, the short fibers F are oriented substantially inthe tire circumferential direction.

A middle part of the sidewall rubber Gs where the bending deformationduring running is largest, is formed by winding the thick tape so thatthe degree of orientation of the short fibers decreases. Accordingly, aless oriented middle part A2 is formed and a high oriented part A1 isprovided on each side thereof. Such less oriented middle part A2 ispreferably provided in a radial height range S1 between 65% and 35% ofthe tire section height H. Therefore, the ride comfort and rollingresistance may be improved. The degree of orientation can be changedstepwise as shown in FIG. 7 a or gradually as shown in FIG. 7 b. In FIG.7 a, a less oriented part A2 is further provided at the radially outerend of the sidewall rubber which is positioned under the belt edge 7 eso as to function as the cushion rubber Gtc.

As to the difference of the actual direction of the fiber from the tirecircumferential direction, it is preferable that at least about 90% ofthe short fibers are less than 30 degrees in order to derive adirectional reinforcing effect from the oriented short fibers.

In this example, as the short fibers F in the sidewall rubber Gs areoriented substantially in the tire circumferential direction, thesidewall rubber Gs is effectively increased in the circumferentialrigidity without excessively increasing the radial rigidity. As aresult, the rolling resistance of the tire is reduced withoutdeteriorating the ride comfort. Also the cut resistance is improved.Further, it becomes possible to reduce the tire weight because thethickness of the sidewall rubber may be decreased by the increasedrigidity.

If the average fiber length is less than 0.2 mm and/or the average fiberdiameter is less than 10 micrometers, it is difficult to obtain asufficient directional reinforcing effect. If the average fiber lengthis more than 5 mm and/or the average fiber diameter is more than 100micrometers, the adhesion to rubber tends to decrease and the wearresistance and crack resistance are liable to decrease.

If the content of the short fibers F is less than 10 parts by weight,the circumferential rigidity of the sidewall rubber 9 decreases. If thecontent of the short fibers F is more than 30 parts by weight, there isa tendency to decrease the crack resistance.

In the above-mentioned embodiment, the fiber containing rubber tape Trfis used to make the entirety of the sidewall rubber Gs which is disposedadjacently to the carcass. However, it is also possible to use the fibercontaining rubber tape Trf to make a part of the sidewall rubber Gs. Inthis case, the remaining part may be formed by winding a pure rubbertape Tp. Further, it is also possible to use a rubber strip extruded ina final shape (not a rubber tape Tp wound into a final shape).Furthermore, a cord-reinforced rubber tape Trc may be used.

Incidentally, regardless of whether the degree of orientation isvariable or constant, a fiber containing rubber tape Trf can be used incombination with a pure rubber tape Tp and/or a rubber strip to make apart or the entirety of a rubber component.

For example, as shown in FIG. 8 (this tire has an aspect ratio of notmore than 55%), the sidewall portion 3 may have a double layeredstructure comprising a sidewall rubber Gs formed by winding a purerubber tape Tp and an inner sidewall rubber Gsin formed by winding afiber containing rubber tape Trf.

In this example, the pure rubber tape Tp is made of a relatively softrubber compound so that the sidewall rubber Gs has a JIStype-A-durometer hardness of from 48 to 58 degrees preferably 50 to 56degrees more preferably 52 to 54 degrees, and a modulus at a 230%elongation of from 1.5 to 2.5 MPa, and a Mooney viscosity of from 28 to44 {ML(1+4)} preferably 34 to 38 {ML(1+4)} more preferably 32 to 40{ML(1+4)}. In the case of a double layered structure, the sidewallrubber (axially outer layer) can have a 230% modulus of from 1.5 to 6.0MPa. This soft rubber compound preferably includes, as its base rubber,diene rubber such as natural rubber, isoprene rubber, styrene butadienerubber, butadiene rubber, chloroprene rubber, acrylonitrile butadienerubber and the like, alone or in combination. The following table showsan example of the soft rubber compound

Butadiene rubber 55 PHR Natural rubber 35 PHR Isoprene rubber 10 PHR FEF45 parts by weight

As to the inner sidewall rubber Gsin, on the other hand, in order toeffectively reinforce the sidewall portion, the short fibers should beoriented in a high degree such that at least about 90% of the shortfibers are oriented at less than 30 degrees with respect to the tirecircumferential direction. For example, aramid short fibers are used.Preferably, the rubber compound for the inner sidewall rubber has a JIStype-A-durometer hardness of from 60 to 95 degrees, a modulus at a 230%elongation of from 2.8 to 6.0 MPa, and a Mooney viscosity of from 40 to73 {ML(1+4)}.

The thickness t2 of the sidewall rubber Gs is set in a range of morethan 0.05 times and less than 4.0 times the thickness t1 of the innersidewall rubber Gsin.

As the unvulcanized rubber tape Tp of the sidewall rubber Gs is made ofthe soft rubber compound, the adhesion between the windings of therubber tape is improved. Thus the occurrence of cracks in the sidewallouter surface can be effectively prevented, though the windings areexposed. Further, as the inner sidewall rubber Gsin increases in therigidity, the steering stability can be improved.

If the JIS type-A-durometer hardness of the soft rubber compound is lessthan 48 degrees, it becomes difficult to maintain a necessary bendingrigidity of the sidewall portion 3 and the steering stabilitydeteriorates. If the JIS type-A-durometer hardness is more than 58degrees, cracks are liable to occur in the sidewall outer surface alongthe boundaries between the windings.

If the 230% modulus of the soft rubber material R1 is less than 1.5 MPa,it becomes difficult to improve the steering stability. If the 230%modulus is more than 2.5 MPa, cracks are liable to occur.

If the Mooney viscosity of the soft rubber material R1 is less than 28{ML(1+4)}, it is difficult to give the predetermined shape to thewindings of the rubber tape. If the Mooney viscosity is more than 44{ML(1+4)}, the adhesion between the windings decreases and cracks areliable to occur.

FIG. 9 shows a modification of the above-mentioned double layeredstructure, wherein the sidewall rubber Gs may be the same as above, butthe inner sidewall rubber Gsin is formed by winding a cord-reinforcedrubber tape Trc shown in FIG. 1 c. The cord-reinforced rubber tape Trcmay be wound in an upper sidewall portion near the tire shoulder. In theremaining lower sidewall portion, the above-mentioned fiber containingrubber tape Trf or the under-mentioned pure rubber tape Tp4 may bewound. In this case, the steering stability may be further improved. Forthe reinforcing RC, organic cords, for example, 840d nylon cords arepreferably used.

FIG. 10 further shows a modification of the double-layered structureshown in FIG. 9, wherein the sidewall rubber Gs is the same as above,but the inner sidewall rubber Gsin is formed by winding a pure rubbertape Tp4 which is made of a rubber compound harder than that of thesidewall rubber Gs for the purpose of increasing the rigidity of thesidewall portion 3. Furthermore, instead of winding the narrow purerubber tape Tp4, the inner sidewall rubber Gsin may be formed byapplying a relatively wide rubber strip which may be formed by means ofan extruder. In the inner sidewall in this example, the JIStype-A-durometer hardness, 230% modulus and Mooney viscosity are set tobe higher than the sidewall rubber Gs and near the respective upperlimits, namely, 95 degrees, 6.0 MPa and 73 {ML(1+4)}.

1. A method of manufacturing a pneumatic tire, comprising: assemblingtire components including a carcass and unvulcanized rubber componentsto make a green tire, the tire comprising the carcass extending betweenbead portions through a tread portion and sidewall portions, an axiallyouter sidewall rubber disposed in each said sidewall portion to definean outer surface of the sidewall portion, and an axially inner sidewallrubber disposed on the axially inside of said axially outer sidewallrubber, vulcanizing the green tire to form said pneumatic tire, whereinthe method further comprises: winding at least one unvulcanizedfiber-reinforced rubber tape having short fibers mixed therein so thatthe windings collectively have a predetermined cross sectional shape ofsaid axially inner sidewall rubber to thereby make the axially innersidewall rubber, wherein the short fibers therein are oriented towards atire circumferential direction, and a degree of orientation of the shortfibers decreases at a middle of the sidewall portion, and winding anunvulcanized rubber tape so that the windings collectively have apredetermined cross sectional shape for at least one of the unvulcanizedrubber components to thereby make said at least one of the unvulcanizedrubber components, wherein said at least one of the unvulcanized rubbercomponents is said axially outer sidewall rubber having a Mooneyviscosity of from 28 to 44 {ML(1+4)}.
 2. The method according to claim1, wherein the tire further comprises a cushion rubber disposed betweenthe carcass and an edge of a tread reinforcing belt, and said at leastone of the unvulcanized rubber components formed by winding saidunvulcanized rubber tape, further includes the cushion rubber.
 3. Themethod according to claim 1, wherein the tire further comprises: aninner liner rubber disposed inside a carcass along the inner surface ofthe tire; an insulation rubber disposed in a radially outer part of thesidewall portion between the carcass and the inner liner rubber; and acushion rubber disposed between the carcass and an edge of a treadreinforcing belt, said at least one of the unvulcanized rubbercomponents formed by winding said unvulcanized rubber tape, furtherincludes the insulation rubber and the cushion rubber, and the methodfurther comprises winding another unvulcanized rubber tape made of anair-impermeable rubber compound to make the inner liner rubber.
 4. Themethod according to claim 1, wherein the tire further comprises: aninner liner rubber disposed inside a carcass along the inner surface ofthe tire; and an insulation rubber disposed in a radially outer part ofthe sidewall portion between the carcass and the inner liner rubber,said at least one of the unvulcanized rubber components formed bywinding said unvulcanized rubber tape, further includes the insulationrubber, the method further comprises winding another unvulcanized rubbertape made of an air-impermeable rubber compound to make the inner linerrubber.
 5. The method according to claim 3 or 4, wherein said at leastone of the unvulcanized rubber components formed by winding saidunvulcanized rubber tape is made of a rubber compound including at least2.5 parts by weight of an age resistor with respect to 100 parts byweight of rubber which includes 40 to 100 parts by weight of lowviscosity polybutadiene rubber, and has a JIS type-A-durometer hardnessof not more than 65 degrees and a 100% modulus of 0.5 to 2.5 MPa.
 6. Themethod according to claim 1, 2, 3, or 4, wherein the tire furthercomprises a clinch rubber disposed in a bead portion of the tire alongthe axially outer surface and bottom face of the bead portion, themethod further comprises winding an unvulcanized rubber tape to make theclinch rubber.
 7. The method according to claim 1, wherein the axiallyouter sidewall rubber has a JIS type-A-durometer hardness of from 48 to58 degrees, and a 230% modulus of from 1.5 to 6.0 MPa.
 8. The methodaccording to claim 1, wherein the unvulcanized fiber-reinforced rubbertape having the short fibers mixed therein has a thickness of 0.3 to 2.5mm, the short fibers have an average length of 0.2 to 5 mm and anaverage diameter of 10 to 100 micrometers, the content of the shortfibers in the rubber compound is 10 to 30 parts by weight with respect100 parts by weight of the base rubber thereof.
 9. The method accordingto claim 1, wherein the pneumatic tire has an aspect ratio of not morethan 55%.
 10. A method of manufacturing a pneumatic tire, comprising:assembling tire components including a carcass and unvulcanized rubbercomponents to make a green tire, the pneumatic tire comprising thecarcass extending between bead portions through a tread portion andsidewall portions, an axially outer sidewall rubber disposed in eachsaid sidewall portion to define an outer surface of the sidewallportion, and an axially inner sidewall rubber disposed on the axiallyinside of said axially outer sidewall rubber; and vulcanizing the greentire to form said pneumatic tire, wherein the method further comprises:making said axially inner sidewall rubber by winding an unvulcanizedrubber tape so that the windings collectively have a predetermined crosssectional shape of the axially inner sidewall rubber, wherein theunvulcanized rubber tape has short fibers mixed therein and the shortfibers are oriented towards the longitudinal direction of the tape witha variable degree of orientation so that the degree of orientation ofthe fibers decreases at a middle of the sidewall portion, and makingsaid axially outer sidewall rubber by winding another unvulcanizedrubber tape so that the windings collectively have a predetermined crosssectional shape of the axially outer sidewall rubber.
 11. The methodaccording to claim 10, which further comprises changing saidunvulcanized rubber tape with the short fibers therein in respect ofsaid degree of orientation of the short fibers.
 12. A method ofmanufacturing a pneumatic tire, comprising: assembling tire componentsincluding a carcass and unvulcanized rubber components including asidewall rubber to make a green tire, the pneumatic tire comprising thecarcass extending between bead portions through a tread portion andsidewall portions, and the sidewall rubber disposed on the axiallyoutside of the carcass in each said sidewall portion to define an outersurface of the sidewall portion; and vulcanizing the green tire to formsaid pneumatic tire, wherein the method further comprises: making saidsidewall rubber by winding an unvulcanized rubber tape so that thewindings collectively have a predetermined cross sectional shape of thesidewall rubber, wherein the unvulcanized rubber tape has short fibersmixed therein and the short fibers are oriented towards the longitudinaldirection of the tape with a variable degree of orientation so that, inthe sidewall rubber, the degree of orientation of the fibers towards thetire circumferential direction decreases at a middle of the sidewallportion.